Final answer:
The bright radio waves from pulsars are caused by strong magnetic fields which accelerate electrons to high speeds, resulting in synchrotron radiation detectable as pulses when the beam crosses Earth.
Step-by-step explanation:
The bright beaming of radio waves coming from pulsars is caused by strong magnetic fields. Pulsars are a type of neutron star, which is the superdense remnant of a massive star that has exploded in a supernova. These compact stars have incredibly intense magnetic fields that can accelerate electrons to very high speeds. When these electrons spiral around the magnetic field lines, they emit synchrotron radiation, which is a broad spectrum of electromagnetic radiation that includes radio waves. This radiation beams out from the pulsar's magnetic poles and sweeps across space like a lighthouse beam. When the Earth is in the path of this beam, we detect the radio waves as pulses, which is why neutron stars of this kind are called pulsars.